The PI to be supported by this application is an assistant professor of Neurology and Otorhinolaryngology at the U. of Pennsylvania, having completed an MD, Ph.D. with Dr. Bernard Cohen, a neurology residency and post-doctoral fellowship in neuro-otology with Dr. David Zee. The candidate has been provided with space and funds to equip a laboratory for research in human vestibular and ocular motor neurophysiology. Under the mentoring of Dr. V. Kumar in the Dept. of Applied Mechanics and Dr. Neil Shepard in the Dep. of Otolaryngology, the PI will learn the principles and techniques of biomechanical modeling, as well as control systems theory. A novel vestibular stimulator has been designed by the PI which will deliver linear and angular accelerations, together or separately, to standing human subjects. Control of this apparatus and analysis of eye, head and trunk postural responses will require further career development through collaboration with mentors. There are 3 specific aims: number 1 is to determine whether the head is stabilized in a body or spatial reference frame during pivot turns. Number 2 seeks to determine the transfer functions describing the motion of body segments during passive vertical axis rotation, so that the role of vestibular information in the control of joint muscle torques may be modeled. In number 3, the behavioral response to step perturbations of the support surface during pivot turns will be compared to simulations, to determine if the model's predictions fit the observations. The long-term goal is development of rational rehabilitation techniques for patients with dysequilibrium following vestibular injury, and to better understand the role of labyrinthine information in postural control during turns. Career goals are to become an independent clinician-investigator by developing a greater familiarity with engineering concepts, to train graduate students and fellows in basic science, and neurology and otolaryngology residents in clinical aspects of neuro-otologic function and disease.